The peak on Steam alone today was 6,192,602 players.
Here are some other statistics, somewhat outdated, but shows the trend:
PC games played by year, with % change from previous year.
2005 568,968
2006 558,074 (-2%)
2007 2,920,185 (+423%)
2008 5,857,447 (+101%)
2009 6,187,437 (+6%)
2010 15,728,587 (+154%)
2011 29,631,542 (+89%)
2012 33,355,879 (+13%)
Console games played by year, with % change from previous year.
All Nintendo, Microsoft, and Sony combined, including portables.
Hardware listed is the year in which the hardware was released.
2005 48,621,847 XBox 360, PlayStation Portable 1000
2006 140,890,341 (+290%) DS Lite, PlayStation 3, Wii
2007 321,998,102 (+229%) PSP 2000, PlayStation Eye
2008 578,241,141 (+80%) PSP 3000
2009 570,507,923 (-3%) DSi, DSi XL, PSP Go, PS3 Slim
2010 614,779,227 (+8%) Kinect, 360 Slim, Playstation Move
2011 578,873,094 (-6%) 3DS, Wii Family Edition
2012 445,278,842 (-23%) 3DS XL, PlayStation Vita, Wii Mini, Wii U
Some observations:
In 2005, PC popularity was 1.17% of consoles.
In 2012, PC popularity was 7.49% of consoles.
+5863% PC gain from 2005 to 2012.
+916% combined console gains from 2005 to 2012.
PCs have increased six times as much as consoles have.
PCs are trending up much faster than consoles.
Source:
http://www.steamgifts.com/forum/YAKms/2005-2012-pc-vs-console-gaming-population-growth-rates
I won't because give my opinion on PCs vs consoles because I don't want to start a flame war or anything...